Mini-excavator is a work machine having a relative small weight (e.g. less than 1.8 tons) and voted to earth moving.
Mini-excavator essentially comprises a machine base rotatably mounted on an undercarriage movable thanks to moving means, e.g. track bands, and a work blade, also known as dozer, pivotally carried by a boom which is pivoted with respect to the machine base.
Width of undercarriage may be varied in function of the space through which the mini-excavator must pass. Indeed, in certain situation undercarriage should be retracted to a minimum width, e.g. during the passage in a narrow space, or should be extended to a maximum width, e.g. when a great stability is needed. Dozer may be controlled by controlling the operation boom.
The above described operation of undercarriage and dozer are hydraulically operated thanks to an hydraulic arrangement essentially comprising a hydraulic cylinder configured to operate boom carrying the dozer, a hydraulic cylinder configured to vary the width of the undercarriage and a selection valve configured to switch the passage of operating fluid so as to control only one of the two aforementioned cylinders.
Such selection valve is placed in the machine base and therefore at least four hoses (two per cylinder), suitable for the passage of high pressure fluid, have to be provided between selection valve and cylinders. Such hoses may be subject to loads and wear due to their long path from valve to cylinders.
Moreover hoses have to pass through a swivel joint which connects machine base to the undercarriage and allows the relative motion of machine base with respect to undercarriage. Therefore, swivel joint needs to be dimensioned to allow the passage of at least such four hoses, therefore increasing its costs and dimensions.
In view of the above, the need is felt to reduce the number of hoses passing through the swivel joint of a mini-excavator for controlling the hydraulic cylinders which control the dozer and the width of the undercarriage. Moreover, the need is felt to simplify the control of the two aforementioned cylinders in an economic way.
An aim of the present invention is to satisfy the above mentioned needs.